Jim Reilly recently documented some of what he has learned from studying the role of HVAC operation in managing the environment for preservation. We’d like to share these insights with you.

Energy waste doesn’t self-announce. You have to go looking for it. What comes out of the air diffuser can seem just fine (i.e., what you want or expect) but the work done on the air—and therefore the energy cost—can vary hugely. The mechanical system can be doing all kinds of unnecessary things to the air along the way, and you’d never know it. Inside a typical system are components that work opposite each other (heat / cool, dehumidify / humidify). The most efficient operation is when they only do what they need to do, and nothing more. Inefficient operation is when, for example, air is cooled more than it needs to be and then heated back up immediately after. How common are such scenarios? Very common. How do you find out if they are going on? You place dataloggers inside air handlers (AHUs) and in ducts to monitor the individual energy-consuming elements. Then you look for one-foot-on-the-gas, one-foot-on-the-brake situations. Experience shows that about 30% of energy cost is due to such suboptimal operation.

Buildings often have a surprising ability to ‘coast’ when systems are turned off. Many (but not all) buildings will gracefully maintain temperature and RH conditions over a period of time if there is a malfunction or intentional shutdown of HVAC systems. This is something quite familiar to facilities staff. Malfunctions such as coil leaks, motor failures, broken belts, and valve failures happen with some frequency. When they cause a whole system to shut down, it becomes an opportunity to observe how the building performs on its own. Often much less happens than one would expect. Of course, building characteristics, local climate, and time of day or season of the year do matter. But for the most part, intentional shutdowns overnight or aggressive slowdown of fans are worth exploring because they often have only minor effects but can save a lot of energy.

‘Flat-lined’ 70 °F (21 °C) and 50% RH aren’t the best conditions for everything. Collection objects decay through pathways that are strongly affected by both temperature and RH. Although 50% RH is not a harmful condition for most kinds of objects, a temperature of 70° F (21° C) might be too warm for effective preservation of materials that degrade through spontaneous chemical reactions. Examples of such materials are acidic paper, organic dyes, and many types of plastics. In addition, unnecessary flat-lining is antithetical to sustainable operation.

Follow the moisture—pay attention to dew point. ‘Deep Throat’ famously told Bob Woodward in the film All the President’s Men to “follow the money” in order to understand the Watergate Scandal. Likewise, to understand why environmental conditions are what they are—and what you might be able to do about them—you must follow the moisture. Heating or cooling the air is fairly easy to do and straightforward to understand. Moisture control is another matter entirely. This is where it becomes challenging and costly to deliver a good preservation environment for collections. Improper relative humidity (RH) leads to a variety of forms of collection decay, but the surprising thing is that the best way to understand and control RH is to track and analyze dew point. The dew point temperature is an indirect measure of the absolute amount of moisture in the air. Overlaying indoor and outdoor dew point graphs shows the amount of humidification and dehumidification being done. Dew point is the best way to track and manage moisture in an HVAC system.

Collections don’t need to breathe. There is sometimes confusion about ventilation requirements for collections in storage. Collections don't need to 'breathe' in the sense that the objects need fresh air and oxygen just like living organisms do. In fact, reduced oxygen can even be beneficial to preservation for certain materials. Ventilation requirements for collection spaces are determined by three main goals, ensuring good uniformity and mixing of air, supplying sufficient fresh air for human occupants and diluting any volatiles that may arise by out-gassing from collections or building materials. Experience has shown, however, that ventilation rates for collection storage are frequently much higher than they need to be to address these goals. Unnecessary fresh outside air and air circulation can work against sustainable operation, however. Many institutions have found that reduced outside air volumes and air circulation is a useful energy-saving measure.

Dehumidification is the most energy-intensive operation for most HVAC systems. In temperate climates, dealing with the high moisture content of outside air in the summertime is one of the most important functions of HVAC systems. In the absence of a desiccant air dryer, most HVAC systems rely on a process called sub-cooling and reheating to remove moisture from the air (i.e., to dehumidify). This is accomplished by passing air over a cooling coil that has cold water circulating through it. To dehumidify the air successfully, the coil has to ‘fight’ two kinds of heat. The first, known as sensible heat, is the kind you can measure with a thermometer. Air containing water vapor has a second kind, called latent heat. This is a large quantity of heat that was given to the water vapor when it originally went from the liquid state to the gaseous state. Water in the vapor phase ‘locks in’ the heat it took to evaporate the water in the first place. When the cooling coil tries to dehumidify the air, it has to provide cooling to overcome both the sensible and the latent heat loads. In practice, this means you have to use some cooling to bring the temperature down and lots of cooling to wring the moisture out. Because you can’t supply this very cold air to the space, you then have to heat it back up to a suitable temperature. The net result is that dehumidification is quite energy-intensive—but vitally necessary for many collection environments.

No two HVAC systems are alike. Just as with people, there are many superficial similarities among individual air conditioning systems. They may even have exactly the same equipment. But when you look closely, they behave differently and have to be studied as unique individuals. Most institutions have systems of varying ages and states of decrepitude. Differences also arise from the way they are programmed (computers run modern HVAC systems) and the varying loads on differing parts of a building. Some work as designed, others don’t. The majority of systems a decade old or more are currently operating in a way noticeably different from what their designer intended. Operators over the years modify either the equipment or the operating program, or both. The result? You have to study each individual system to understand how it is actually working.

There probably isn’t anyone driving the bus. Casual observers might assume that within an institution there is someone who has a holistic overview of what HVAC systems are supposed to be doing (what conditions should they deliver for best collection preservation) as well as how effectively they are meeting the desired goals. This person would, ideally, also keep an eye on energy use. In reality, there usually is not such a person because of the fragmented nature of how systems are specified, designed, installed, operated and maintained. For most of the life of systems, the designer and installer are long gone. The role defined for the operators usually does not include the leisure or the mandate to investigate, diagnose and create a holistic overview. Their role is usually confined to reacting to malfunctions and performing preventive maintenance. The closest thing to the holistic overview resides in the ‘controls person,’ but all too often their role is mainly watching for alarms.

There is no substitute for data. Without a record of environmental conditions nothing can be understood or evaluated about the preservation quality of any collection storage or display environment. It is hard to argue that anything is being effectively managed without some form of measurement of results. For collection environments, that means reliable monitoring close to the collection objects is a necessity, not a luxury. There are very few processes in institutional life that cost so much and are as unexamined as collection storage environments.

There’s usually a correlation between a clean, orderly mechanical room and a well-run facilities department. It’s always an interesting thing to do to visit the mechanical rooms in your institution. Not only do you learn about the equipment and people that operate the building, but you can often see at a glance how much care and attention the systems get. When you see unlabeled piping, dirt, coffee cups, wiring scraps, plumbing debris, dirty filters piled up and general disarray, it’s a good bet that the facilities operation is itself either severely understaffed, badly or indifferently run or otherwise in crisis. It’s not like a cluttered desk—it’s an indication of real problems.